Cardiopulmonary dirofilariasis, (i.e., heartworm disease) is a severe vector-borne helminthiasis of dogs and cats worldwide. It is transmitted by Culicidae (i.e., mosquito) bites and caused by the development of a filarial nematode, Dirofilaria immitis, in the pulmonary arteries and the right ventricle of the heart. Clinically, it leads to irreversible cardiac insufficiency that can result in the death of the animal. Treatment is difficult and prevention is critical for dirofilariasis control.
Current prevention methods are based exclusively on the regular use of macrocyclic lactones to kill infective larvae inoculated by mosquitoes. An exemplary product is HEARTGARD®, which contains ivermectin as the active ingredient against the tissue stage of D. immitis. For about a decade, however, resistant strains of D. immitis have emerged, for example, in the United States, posing a problem for the control of the disease and jeopardizing the registration of new drugs.
The problem of drug resistance with respect to heartworm control is likely to spread in the coming decades. Accordingly, there is a strong need for an alternative prevention program to be used either in conjunction with current therapy or as a standalone treatment. The instant invention meets this need using a novel vaccine strategy to internal targets of D. immitis. 
Other attempts at heartworm vaccines are known in the art. For example, U.S. Pat. No. 4,842,999 to Fuller et al., discloses a vaccine and diagnostic test for canine heartworm. The '999 patent more specifically pertains to cell lines IDi10, which produces the IDi10 monoclonal antibody directed against the 14 kD D. immitis antigen, and IDi76, which produces the IDi76 monoclonal antibody directed against glycoprotein antigens.
Another example, U.S. Pat. No. 5,744,593 to Klimowski et al., discloses parasitic helminth thiol specific antioxidant (TSA) larval proteins; to parasitic helminth larval TSA nucleic acid molecules, including those that encode such TSA proteins; to antibodies raised against such TSA proteins; and to compounds that inhibit parasitic helminth larval TSA activity.
Another example is found in U.S. Pat. No. 5,750,393 to Tripp et al. The '393 patent discloses antibodies raised against parasite astacin metalloendopeptidase and filarid cysteine protease proteins.
WO 1993/010225 to Grieve et al., discloses a vaccine targeting a protease that is important for life cycle transition in D. immitis. 
Finally, U.S. Pat. No. 4,761,281 discloses a non-toxic amount of water-soluble fraction of an extract of adult Dirofilaria organisms and of an acid-soluble fraction of an extract of adult Dirofilaria organisms for use as a vaccine.
None of the above references or references not mentioned herein has produced a viable commercial product. Most efforts so far have focused on incoming L3s larvae or recombinant antigens from L3. These antigens were typically excretory-secretory antigens from the larvae epicuticle/cuticle. They are immunogenic in dogs but poorly so due to their immunosuppressive properties. Furthermore, some of them can be sloughed off leading to immune evasion. Both aspects may explain the limited efficacy of vaccines tested so far. The vaccine compound and method of treatment of the present invention seeks to improve on the prior art in a novel and nonobvious way.